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The concept of topological quantum number, or topological charge, has been used extensively to describe topological defects or solitons. Nematic liquid crystals contain both integer and half-integer topological defects, making them useful models for testing the rules that govern topological defects. Here, we investigated topological defects in nematic liquid crystals using the phase-field method. If there are no defects along a loop path, the total charge number is described by an encircled loop integral. We found that the total charge number is conserved, and the conservation of defects number is determined by a boundary during the generation and annihilation of positive–negative topological defects when the loop integral is confined. These rules can be extended to other two-dimensional systems with topological defects. [ABSTRACT FROM AUTHOR]

SnO2 is regarded as a prospective anode material candidate for high energy density lithium‐ion batteries (LIBs). However, rapid structural degradation and low conductivity always bring about poor cycling stability and electrochemical reversibility, becoming critical dilemmas toward its practical application. To address these issues, herein, a facile multi‐step in situ synthesis protocol is developed to tactfully achieve self‐standing 3D hollow nanoporous SnO2‐modified CuxO nanotubes with nanolamellar metallic Cu inwalls (3D‐HNP SnO2/CuxO@n‐Cu) via chemical dealloying, heat treatment, electrochemical replacement, and selective etching. The results show that the unique 3D‐HNP SnO2/CuxO@n‐Cu as a binder‐free integrated anode for LIBs exhibits superior Li storage properties with high initial reversible capacity of 3.34 mAh cm−2 and good cycling stability with 85.6% capacity retention and >99.4% coulombic efficiency after 200 cycles (capacity decay of only 0.002 mAh cm−2 per cycle). This is mainly attributed to the unique 3D hollow nanoporous configuration design composed of interlinked CuxO nanotubes modified by ultrafine SnO2 nanocrystals (4–10 nm) with two‐way mechanical strain cushion and nanolamellar metallic Cu inwalls with boosted electrical conductivity. This work can be expected to offer an original and effective approach for rational design and fabrication of advanced MOx‐based anodes toward high‐performance LIBs. [ABSTRACT FROM AUTHOR]

The theoretical specific capacity of tin oxide (SnO2) anode material is more than twice that of graphite material (782 vs 372 mAh g–1), whereas its potential usage is limited fatally by its huge volume expansion during lithiation. An effective solution is to encapsulate tin oxide into hollow structure such as yolk‐shell based on the principle of confinement. However, in light of the restricted space of active substance, this kind of hollow electrode always has the low capacity, severely limiting its commercial value. Herein, a peapod‐like Cu‐SnO2@copper foam (CF) as high area specific capacity anode based on the Kirkendall effect, in which the "pod and peas" in the peapod‐like structure are composed of SnO2 and Cu nanoparticles, respectively, is tactfully designed and constructed. Compared to other SnOx‐based electrodes with different hollow structure designs in published reports, the unique peapod‐like Cu‐SnO2@CF anode delivers a remarkably high first reversible capacity of 5.80 mAh cm‐2 as well as excellent cycle stability with 66.7% capacity retention and ≈100% coulombic efficiency after 200 cycles at a current density of 1 mA cm–2, indicative of its quite promising application toward high‐performance lithium‐ion batteries. [ABSTRACT FROM AUTHOR]

In this article, three-dimensional nanoporous Cu/Cu6Sn5 microparticles (3D-NP Cu/Cu6Sn5 MPs) were prepared by one-step chemical dealloying of Cu20Sn80 (at%) alloy slices in a mixed aqueous solution of HF and HNO3 and then filled into a three-dimensional porous copper foam (3D-PCF) skeleton as anode (3D-PCF@Cu/Cu6Sn5) for lithium-ion batteries (LIBs). The results show that the ellipsoidal 3D-NP Cu/Cu6Sn5 MPs with feature sizes of 3 to 8 μm are composed of numerous uniform nanoparticles (100 to 200 nm) and plenty of voids. Compared with similar Sn-based electrodes in this work and other published reports, the as-prepared electrode delivers more outstanding electrochemical performance with a superior reversible capacity of 1.90 mAh cm−2, 84.44% capacity retention and > 99.5% coulombic efficiency upon 200 cycles. The cycling stability and integrity of the overall structure of the composite electrode have been greatly enhanced under the synergistic effect of the buffer effect of copper as the inactive component, the unique hierarchical porous electrode architecture and the effective limitation in three dimensions of the 3D-PCF skeleton. We are confident that this work can provide new-generation LIBs with a promising anode candidate and a facile method of dealloying, and a subsequent filling step can achieve the practical production and application of high-performance LIBs. [ABSTRACT FROM AUTHOR]

Structural deterioration and low conductivity are key factors that give rise to severe capacity fading of transition metal oxides as anodes for lithium-ion batteries (LIBs). An effective way to overcome this challenge is to construct nanosized metal oxide heterostructures integrated with a 3D nanoarchitectured metal matrix to buffer volume variation, reinforce structural stability and improve electronic conductivity. Herein, a facile and effective underpotential oxidation (UPO) assisted dealloying protocol has been developed successfully to synthesize freestanding monolithic 3D nanoporous copper@1D cuprous oxide nanowire network (3D NPC@1D Cu2O NWN) heterostructures. Based on their dealloying behavior, the evolution law can be well established, sequentially described as “dealloying of (Mn, Cu) accompanying Cu2O NW germination”, “growth of Cu2O NWs accompanying (Mn, Cu) re-dealloying” and “Cu2O NWN coarsening”. Compared to other CuxO-based electrode materials with different structural designs reported in the literature, the unique nanocomposites as an anode for LIBs exhibit far superior Li storage performance including an ultrahigh initial reversible capacity of 2.71 mA h cm−2, good cycling stability with 60.2% capacity retention after 150 cycles (just 0.007 mA h per cm2 per cycle for capacity fading), and excellent rate capability with reversible capacity as high as 1.64 mA h cm−2 after 55 high-rate cycles. This mainly originates from effectively accommodating huge volume changes during charge/discharge processes, providing abundant reaction active sites, shortening electron/ion transport paths, and building a reliable 3D/1D composite nano-configuration without additional binders and conductive agents, indicative of a considerably promising anode candidate for high-performance LIBs. [ABSTRACT FROM AUTHOR]